Wound series capacitor



Doc. 29, 1964 s. o. LINDERHOLM nouun ssaxss cmcrroa Filed Nov. 3. 1959 a\llfl) 1 5 I /1 r I 3 W] I W 9 3 3. m a a l F w m w I'R/J 3 I 5 o F 5 L.fi l INVENTOR. svm 0. LINDERHOLM ATTORNEY United States Patent Oificc3,163,807 Patented Dec. 29, 1964 3,163,807 WOUND SERIES CAPACITOR SvenO. Linderholm, Ludvilra, Sweden, assignor to The Ohio Brass Company,Mansfield, Ohio, a corporation of New Jersey Filcd- Nov. 3, 1959, Ser.No. 45,253 7 Claims. (Cl. 3l7--260) This invention relates to capacitorsand, more particularly, to grading capacitors and high voltagecapacitors.

It is known in the electrical art to use capacitors for gradingelectrical stresses in potheads and bushings. For such purposes, it isalso known to utilize capacitors having multiple overlapping foils forincreased utilization of the dielectric material and for producingdesired capacitance and voltage withstand for prescribed physicaldimensions. With such arrangements, shunt connections have been employed between the ends of the individual foils in order to reduce theinductance of the capacitor.

I have devised and described herein an improved capacitor of the typejust referred to, but one incorporating a greatly simplified arrangementof the shunt connections between the foils. The arrangement is such thatsignificant economies in the manufacture of the capacitor are possible.

It is a general purpose of the invention to provide improved capacitorsuseful for voltage division and potential grading functions.

The invention, together with further objects, features and advantagesthereof, will be more fully understood by reference to the followingdetailed specification and claims, taken in connection with the appendeddrawings, in which FIG. 1 is a side elevation view of the capacitor ofthe invention;

FIG. 2 is a sectional view of the capacitor of FIG. 1, taken in thedirection 2-2;

FIG. 3 is a schematic diagram, in longitudinal developmerit, showing thefoil arrangement of the capacitor of FIG. 1 according to one embodimentof the invention; and

FIG. 4 is a schematic diagram similar to that of FIG. 3 illustrating thefoil arrangement of the capacitor according to another embodiment of theinvention.

As shown in FIGS. 1 and 2, the capacitor is in generally annular formconstituted by a cylindrical roll of foil and paper. The inner part ofthe capacitor, indicated at 11, is a paper tube or other core forsupported the capacitor, and the outer part, indicated at 12, is awinding of paper or the like for protecting the capacitor. The centralpart of the capacitor, designated at 13, is a continuous winding of amulti-layer of foil and paper.

Connections are made to the foils of the multi-layer by means of narrowstrips of metallic material such as foil, referred to herein as tabs,which extend into the multilayer to contact the foils thereof. Two tabs14 and 15 are connected to the foils at the inner and outer extremitiesof the multi-layer which forms the central part 13 of the capacitor.Other tabs 16 to 26, inclusive, extend from between the foil and paperof the multi-layer to the exterior of the winding, in a radialdirection, and back between the foil and paper to interconnect separatefoils which function as armatures for the capacitor. The interconnectionof the foils serves to reduce the inductance of the capacitor, as ishereinafter described.

The capacitor 10 is utilized as a grading capacitor in terminatingdevices such as potheads, and the inner radius of the capacitor is suchthat the capacitor may be received over the core of the pothead. i

In FIG. 3 the foil and paper multi-layer 28 is shown in longitudinalsection, with the individual layers in somewhat schcmatic form andspaced apart for convenience of illustration and description. Theseveral layers 29 to 33 of the multi-laycr 28 are wound together intightly superimposed and interleaved relationship to constitute thecapacitor 10 of H6. 1. as is known in the art pertaining to rolledcapacitors. The one end of the multi-layer 28, referred to as the innerend of the multi-layer, is desig nated by the numeral 34, whereas theremaining end of the multi-layer, referred to as the outer end of themultilayer, is designated by the numeral 35.

The layers 29, 30 and 31 are each constituted by one or more sheets ofpaper, preferably in continuous strips for convenience of winding. Thelayers 29 and31 are designated as insulating layers or layers ofinsulating paper inasmuch as the paper functions to insulate the foilsof successive turns each from the other. The layer 30 is designated as adielectric layer or layer of dielectric paper inasmuch as the paperfunctions as a dielectric medium between the two foil layers in theutilization of the device as a capacitor. The paper has suitableinsulating and dielectric properties, such as a high density capacitorpaper known in the art.

The layers 32 and 33 are designated as foil layers, each layer beingconstituted by a plurality of sheets of metallic foil, or foils, whichare opposed with respect to the dielectric layer 30 to constitute thearmatures of a plurality of interconnected capacitors. The layer 32comprises a succession of foils 36, 37, 38, 39 and 40 and 41 ofsubstantially the same length and having a predetermined spacing betweenthe adjacent ends of successive foils. The

layer 33 comprises a succession of foils 42, 43, and 44 and 45 arrangedbetween the adjacent papers of the dielectric layer 32 and theinsulating layer 33 and opposite the foils 36 and 37, 38 and 39, and 40and 41, respectively.

The foils of the foil layer 33, in each instance, are associated withtwo foils of the foil layer 32. For example, the foil 42 extends for thelength of the foils 36 and 37 along the dielectric layer 30 on theopposite side of that layer from the foils 36 and 37. The two halves ofthe foil 42 cooperate as capacitor armatures with the foils 36 and 37.However, since the foil 42 is in one piece, the armatures constituted bythe foil 42 are connected electrically in series and the two capacitorsformed by the foils 36 and 42 and 42 and 37 are also connected inseries. These foils, referred to herein as a foil group, and thesuccessive foils of the foil layers 32 and 33 are arrangedintosuccessive foil groups, each incorporating the same arrangement offoils.

The successive foil groups, just referred to, are connected in series bythe tabs 16 to 26. Thus in FIG. 3 the tab 16 connects the inner end ofthe foil 37 t0 the outer end of the foil 38 so that the capacitorsconstituted by I the foil groups 36, 42, 37 and 38, 43, 39,respectively,

are connected in series. Similarly, the tab 17 connects the inner end ofthe foil 39 and the outer end of the foil 40 to connect the capacitorsconstituted by the foil groups 38, 43, 39 and 40, and 44 in series. Theremaining foil associated with the foils 40 and 44 is not shown, thefoils 41 and 45 constituting the final foils at the outer end 30 of themulti-layer.

As shown, particularly in FIGS. 1 and 2, each of the tabs 16 to 26 isconstituted by a strip of sheet conducting material, such as a metallicfoil formed of somewhat heavier material than, or several layers of thesame material as, the foils 36 to 45. In each instance the tabs contactthe end of the foil along the width of the tab and along the transverseor longitudinal dimension of the foil and extend outwardly and radiallyabout the intervening papers and inwardly to contact the associatedfoil. The length of the foils is determined with respect to thecircumference so that the corresponding extremities of the foils whichare interconnected by the tabs are disposed in radially overlappingrelationship.

The terminal tabs 14 and 15 are arranged to contact the outer end of thefoil 36 and the inner end of the foil 41, respectively. However, the tab14 extends in one direction and the tab 15 in the opposite directionfrom the winding. The capacitor is usually associated with othercapacitors of the same kind by stacking along the longitudinal axis andthis arrangement of the terminal tabs facilitates interconnection of theseveral capacitors.

With the arrangement of foils shown, the flow of charging current in onedirection in the foils of the layer 32 is paralleled by a flow in theopposite direction of the charging current in the associated foil of thelayer 33. Accordingly, the net magnetic field produced by the flow ofcurrent to and from the capacitor and the inductive ellect of thewindings is of a very low order of magnitude.

Because of the rolled arrangement of the winding, it will be understoodthat the layers 29 and 31 of the insulating paper may be combined into asingle layer. Winding and tab insertion may be facilitated, for example,by omitting the layer corresponding to the layer 29 and utilizing only alayer 31 of appropriate insulating strength. Thus, in the exemplaryembodiment of the invention, referred to hereinafter, only the layers 30and 31 of insulating paper were used, each constituted by seven layersof kraft capacitor paper.

Manufacture is advantageously accomplished by means of a winding machinein which the foils and papers are carried as continuous strips on aplurality of spools. The capacitor is wound upon the inner part or core11 which is carried upon an electrically driven spindle. In winding, theends of the paper strips which form the layers 29, 30 and 31 or thelayers 30 and 31, as the case may be, are attached to the part 11 and asufiicient number of turns wound to provide a secure anchoragethereupon. The ends of the foil strips which form the foil layers 32 and33 are then inserted on opposite sides of the paper strips which formthe layer 30, and the winding continued until the foil strip of thelayer 32 has reached a predetermined length to constitute the foil 36.The foil strip is then cut and the tab 14 inserted between the foil 36and the paper of the layer 29, adjacent the outer end of the foil.

The winding is then continued through a predetermineddistance,corresponding to the spacing between the adjacent ends of the foils 36and 37, whereupon the foil strip of the layer 32 is again insertedbetween the papers of the layers 29 and 30, with one end of the tab 16in contact with the foil 37, adjacent the inner end. After apredetermined distance, both foil strips are cut to complete the foils37 and 42, and winding is then continued.

Again, after a predetermined distance, the foil strips are started toform the foils 38 and 43 and the winding is continued until the foil 38is of the correct length. The foil strip is then cut and the tab 16reinserted between the layers 30 and 32 to contact the foil 38 adjacentthe I outer end of the foil. The process is repeated until the foil 41has been started and tab inserted from the side of the capacitoropposite to the tab 14 to contact the inner end of the foil 41. The foilstrips are then cut to form the foils4l and 4S and winding is thencontinued with only the paper layers to form the outer part 12 of thecapacitor. The final turns of paper are then secured in place. The finalwinding may be varnished, impregnated, or otherwise prepared for theintendcd'use.

'Since the metallic strips which constitute the tabs 16 to 26 are alwaysinserted between the paper and the foil from the same side of thewinding and are always in serted in identical positions. e.g., incontact with the foils of the layer 32, the interconnection of the foilsmay be accomplished with a relatively small probability of error.Because of the simplicity and consistency of these manuthe winding issimplified by utilizing a single foil in the foil layer 46 in adjacentgroups of foils. As shown, interconnection of the foil groups,constituted by the foils 48, 49 and and 50, 51 and 52, is accomplishedby the tab 53. The common foil 50 serves as another connection betweenthe capacitor groups parallel to the tab 53. However, analysis indicatesthat no current flows in the central portion of the foil 50,- e.g., theportion corresponding to adjacent portions of the foils'37 and 38 inFIG. 3, and tests indicate that inductance of the capacitor of FIG. 4does not differ appreciably from that of the capacitor of FIG. 3.

The arrangement of FIG. 4 has some advantage. from the standpoint ofsimplicity of manufacture, inasmuch as the cutting and spacingoperations are performed upon only one foil at a time. Thus the foils 48and 50 are first formed by cutting and spacing the foil strip of thelayer 46; next the foils 49 and 51 are formed by cutting and spacing thefoil strip of the layer 47; then the-foils 48 and 49 of the layer 46,and so on. Moreover, the fact that the several foils of the two layers,e.g., the foils 48 and 49 and the foils 50 and 51, are of the samelength reduces the possibility of error both in engineering and duringmanufacture.

A grading capacitor embodying the foil arrangement of FIG. 4 in six foilgroups and having a nominal capacitance of .0065 microfarad displayed anatural resonance frequency of 1890 kc./s. by impulse test. The samecapacitor in which the tabs were omitted displayed a natural resonancefrequency of 75.2 kc./s. Having in mind the importance of low inductancein grading capacitors under transient conditions, it is apparent that avery large improvement in result is achieved with a comparatively simpleand inexpensive capacitor construction.

It is to be understood that the foregoing description is not intended torestrict the scope of the invention and that various rearrangements ofthe parts and modifications of the design may be resorted to. Thefollowing claims are directed to combinations of elements which embodythe invention or inventions of this application.

I claim:

1. A capacitor comprising a wound multi-layer of conductive foils andsheet insulating material in the form of an annular roll in which asuccession of first foils on one side of a dielectric layer of saidsheet material are opposed by an associated succession of second foilson the remaining side of the said sheet material, and in which each ofthe said second foils is disposed opposite two of the foils of the saidfirst foils, and interconnecting means between the initial end of onefoil and the final end of a succeeding foil of the said first foils,comprising a conductive tab extending from the foil to the exterior ofthe multi-layer through a radial interval of the roll and into themulti-layer to contact the said succeeding foil.

2; A capacitor comprising a wound multi-layer of conductive foils andsheet insulating material in the form of an-annular roll in which asuccession of first foils on one side of a dielectric layer of the saidsheet material are opposed by an associated succession of second foilson the remaining side of the said sheet material, a first terminal forthe capacitor comprising a conductive tab connected to a first one ofthe said first foils, a second terminal for the said capacitorcomprising a conductive tab connected to a last one of the said firstfoils, and interconnecting means between the initial end of one foil andfacturing operations, the mistakes and consequent delays of the priorpractices are substantially eliminated.

In the embodiment of the invention shown in FIG. 4,

the final end of a succeeding foil of successive pairs of theintervening foils of the said first foils. 3. The invention inaccordance with claim 2, the said interconnecting means each comprisinga conductive tab extending transversely through the said multi-layer tothe exterior thereof, radially of the roll, and then transversely intothe multi-layer.

4. The invention in accordance with claim 3 in which at least theconductive tabs of the said interconnecting means are all disposed atone side of the capacitor.

5. The invention in accordance with claim 4, in which the interconnectedfoils of the said first foils comprise a single conductive piece.

6. A capacitor comprising a continuous winding of a compositemulti-layer constituted by a plurality of sheets of insulating materialand metallic foil, one of the said sheets of insulating material havinga succession of sheets of foil on one side thereof and an associatedsuccession of sheets of foil on the remaining side thereof successivelyoverlapping the said first named sheets of foil to constitute aplurality of series connected armatures having a common dielectriclayer, and shunt connections between the ends of the strips of only thesaid first named succession of sheets of foil to control the currentflow therein and minimize the inductive etfect of the winding.

7. The invention in accordance with claim 6 in which each of the sheetsof foil of the second named succession of sheets has two separate sheetsof foil of the said first named succession of sheets opposed thereto toconstitute two series connected capacitors and in which the said.

shunt connections series-connect the several sets of two capacitors.

References Cited in the tile of this patent UNITED STATES PATENTS2,634,315 Allison Apr. 7, 1953 2,731,706 Grouse Jan. 24, 1956 2,919,390Robinson Dec. 29, 1959 2,930,109 Robinson Mar. 29, 1 960 FOREIGN PATENTS561,258 Great Britain May 11, 1944 1,173,186 France Oct. 27, 1958

1. A CAPACITOR COMPRISING A WOUND MULTI-LAYER OF CONDUCTIVE FOILS ANDSHEET INSULATING MATERIAL IN THE FORM OF AN ANNULAR ROLL IN WHICH ASUCCESSION OF FIRST FOILS ON ONE SIDE OF A DIELECTRIC LAYER OF SAIDSHEET MATERIAL ARE OPPOSED BY AN ASSOCIATED SUCCESSION OF SECOND FOILSON THE REAMAINING SIDE OF THE SAID SHEET MATERIAL, AND IN WHICH EACH OFTHE SAID SECOND FOILS IS DISPOSED OPPOSITE TWO OF THE FOILS OF THE SAIDFIRST FOILS, AND INTERCONNECTING MEANS BETWEEN THE INITIAL END OF ONEFOIL AND THE FINAL END OF A SUCCEEDING FOIL OF THE SAID FIRST FOIL,COMPRISING A CONDUCTIVE TAB EXTENDING FROM THE FOIL TO THE EXTERIOR OFTHE MULTI-LAYER THROUGH A RADIAL INTERVAL OF THE ROLL AND INTO THEMULTI-LAYER TO CONTACT THE SAID SECCEEDING FOIL.